CN104828058A - Method for Checking an Automatic Parking Brake System - Google Patents

Abstract

The invention relates to a method for checking an automatic parking brake system, in particular a method for checking the functional state of an automatic parking brake system with a control unit and a An actuator (2) that generates the electromechanical braking force. The method to be solved by the present invention is to provide a method which can be carried out during driving operation of the vehicle. For this purpose, the control unit activates the actuator ( 2 ) with a frequency lower than that which can cause the actuator ( 2 ) to turn in order to detect a short circuit.

Description

Method for checking the automatic parking brake system

technical field

The invention relates to a method for checking the functional state of an automatic parking brake system, in particular to a method for detecting a short circuit, also to a control and/or regulator and to an automatic parking brake system Braking System.

Background technique

An automatic parking brake (APB) is known, for example, from DE 10 2011 005 842 A1. It includes a control unit which cooperates with two actuators which are respectively arranged on the two rear wheels of the motor vehicle. Such actuators generally involve (DC) electric motors, which move the brake pistons by means of a transmission and a spindle drive in order to apply clamping force to the brake pads. Through this mechanical locking, the automatic parking brake replaces the parking function of conventional hand brakes, which is usually implemented via a cable drive. The control unit for the automatic parking brake is either located in the interior of the vehicle, or it is integrated into an existing controller, for example the driving dynamics controller ESP. In order to activate the two actuators, the control unit is connected to the two actuators via lines arranged in the vehicle, in particular via copper wires. The routing of the cables from the body, in particular from the wheel housings, to the actuators arranged on the rear axle represents a special challenge for the routing of the cables, since the cables are freely accessible at this point and due to environmental influences such as mountain Rock collapse, damp, weasel bites, etc. and bear huge loads. Under such loads, damage to the line may occur, which may lead to a short circuit. This short circuit produces an overcurrent which can permanently impair the operating mode of the parking brake. It is therefore of great importance for the reliable operation of the automatic parking brake to detect possible short circuits in these lines and to signal them to the driver.

In conventional systems, short-circuit detection in the parking brake system is carried out by monitoring the current conducted in the line, so that in the case of a short-circuited actuator an overcurrent is detected and the actuator is therefore switched to no current . However, in order to be able to detect overcurrents as a whole, this monitoring is only carried out in the activated state of the actuator, ie only during stationary operation. It has hitherto not been possible to detect a short circuit between two input lines connecting the actuator to the control unit in the non-actuated state of the actuator. During driving operation of the vehicle, in particular to check for short-circuits in the connecting lines, activation of the actuators may not be possible, since the activation of the actuators assigned to the rear wheels moves the actuators and thus activates the parking function while the vehicle is running.

Contents of the invention

The technical problem underlying the invention is therefore to provide a method for checking the functional state of an automatic parking brake system which can be carried out while the vehicle is in motion.

This technical problem is solved by the features of the independent claims. Developments of the invention are specified in the dependent claims.

The method according to the invention is used for checking the functional state of an automatic parking brake system and in particular for detecting short circuits, wherein the method preferably has a control unit and an actuator for generating an electromechanical braking force, wherein the control The unit triggers the actuator at a frequency higher than that which would cause the actuator to turn. The frequency can be chosen such that it does not substantially affect the stalling of the actuator. The frequency here is preferably selected according to the inertia of the actuator ( 2 ).

The method according to the invention is particularly advantageous because, unlike conventional methods, short-circuit detection is possible even while the vehicle is in motion. The short-circuit measurement can be carried out during operation of the vehicle by the frequency of the trigger signal not causing a rotation of the actuator, which is usually designed as a DC motor. Damage to the circuits of the automatic parking brake system and consequently a loss of function can therefore not be detected when the parking brake is actuated, but advantageously already immediately after the damage has occurred. The frequency of the trigger signal is preferably adapted to the inertia of the actuator in order to avoid movement of the actuator. Furthermore, no additional components are required for the method according to the invention, but such a method can be implemented in the control and/or regulator, for example, in terms of programming.

In this method, the actuator current caused by the high-frequency triggering can advantageously be measured by means of a current measuring unit. The current measuring unit is preferably an existing component of the control unit for calculating the application force of the parking brake, which can be used to detect the current caused by the actuation of the actuator during driving operation. The measured current is evaluated in order to be able to draw conclusions about the operating state of the automatic parking brake system from the detected current. In particular, a comparison with a suitable threshold value can be carried out, which enables a decision on the condition of the parking brake system.

The high-frequency actuator triggering signal is advantageously generated by means of an H-bridge circuit of the control unit, the H-bridge circuit comprising a plurality, in particular four, switching elements. A high-frequency actuator triggering signal is thus produced by suitably high-frequency triggering of the switching element, for example by means of a rectangular signal. The frequency of the actuator triggering signal is correlated here with the frequency of the triggering signal for the switching elements of the H-bridge circuit.

The switching frequency of the switching element and thus the polarity switching frequency of the actuator can advantageously be between 10 kHz and 50 kHz. But the frequency is preferably about 25 kHz. The actuator preferably switches polarity with the frequency of the high-frequency actuator trigger signal. It is important that the frequency is chosen such that the polarity reversal of the motor is done so quickly that the motor may not be able to move due to its inertia when the parking brake system is intact.

In order to be able to draw conclusions about the operating state of the parking brake system from the actuator activation signal, it is preferable to evaluate the actuator current that may be caused by the high-frequency activation. The evaluation can then advantageously draw conclusions about the condition of the line, for example an interruption of at least one line in the line, or a short circuit between the lines, or a normal operating state.

The capacitor, in particular a disturbance suppression capacitor of the actuator, advantageously generates a measurable reactive current in the normal operating state of the parking brake system as a result of the actuator activation signal. In this way, the normal operating state of the automatic parking brake system can be unambiguously identified, since this reactive current cannot be generated in the event of freewheeling or in the event of a line short circuit. The normal operating state of the automatic parking brake can thus be unambiguously inferred when reactive current is present.

It is particularly advantageous if the method for detecting a short circuit is carried out continuously or at periodic intervals during vehicle operation. In this way it is already ensured during the operation of the vehicle that the parking brake is fully operational and that the vehicle can be securely immobilized when parked.

The method according to the invention is executed in a controller or controller of the motor vehicle, which can be a component of an automatic parking brake system.

Description of drawings

Additional features and advantages of the invention emerge from the description of an exemplary embodiment with the aid of the drawings. In the attached picture:

1 is a sectional view of an automatic parking brake for a vehicle with an electric brake motor for generating clamping force to immobilize the vehicle;

Figure 2 is a schematic circuit diagram of a part of the control unit with an H-bridge circuit for triggering the actuators and a current measurement unit for measuring the motor current;

Figure 3 is a schematic backup circuit diagram of an automatic parking brake with a DC motor;

Figure 4 is a schematic backup wiring diagram of an automatic parking brake with a DC motor in a short circuit condition; and

FIG. 5 shows a diagram with the triggering signals of the switching elements of the H-bridge circuit and the resulting actuator currents measured by means of a current measuring unit.

Detailed ways

FIG. 1 shows a sectional view for an automatic (automated) parking brake (parking brake) 1 for a vehicle, which can be performed by means of an actuator 2 (braking brake) currently configured as a DC motor. motor) to apply a clamping force for securing the vehicle. The actuator 2 drives an axially supported spindle 3 , in particular a spindle. On the end of the main shaft 3 facing away from the actuator 2 , the main shaft 3 is equipped with a main shaft nut 4 , which in the pressed state of the parking brake 1 bears against the inner front surface of the brake piston 5 or on the back. The spindle nut 4 is moved axially during the rotational movement of the actuator 2 and during the resulting rotational movement of the spindle 3 . The spindle nut 4 and the brake piston 5 are mounted in a brake caliper 6 which engages the brake pads 7 in a caliper-like manner from above. A brake friction layer 8 , 8 ′ is arranged on both sides of the brake lining 7 .

During the application of the parking brake 1, the electric motor (actuator 2) turns, with the result that the spindle nut 4 moves axially towards the brake pad 7 until the brake pad applies a predetermined maximum clamping force to the on the brake piston 5.

The triggering of the actuator 2 takes place by means of a control unit not shown in FIG. 1 , which may, for example, be a controller of a driving dynamics system such as ABS (Antilock Braking System), ESP (Electronic Stability Program) or EHB (Electrohydraulic Brake )control. FIG. 2 shows a section through such a control unit with H-bridge circuit 9 . The H-bridge circuit 9 comprises a total of four switching elements T1 to T4 , which can be transistors and preferably MOSFETs in particular. The H-bridge circuit 9 generates an actuator triggering signal, which is supplied to the actuator 2 shown in FIG. 1 via lines 13 , 13 ′. The triggering of the H-bridge circuit 9 is effected in such a way that the polarity of the triggering signal is reversed depending on the desired direction of rotation of the actuator 2 . Specifically, in order to generate a first direction of rotation of the actuator 2, the switching elements T1 and T4 are switched conductive and the switching elements T2 and T3 are switched non-conductive, while in order to generate a second opposite direction of rotation of the actuator , the switching elements T2 and T3 are switched conductive and the switching elements T1 and T4 are switched non-conductive.

Furthermore, the control unit includes a current-measuring unit 11 , which now has a shunt resistor R connected in the supply path U _b of the H-bridge circuit 9 . The shunt resistor R is connected to a measuring signal amplifier 17 for measuring the current (actuator current) induced by the actuation of the H-bridge circuit 9 and received by the actuator 2 . During normal operation of the parking brake, the actuator current is used to determine the clamping force of the actuator by means of a suitable algorithm.

FIG. 3 shows a schematic alternative circuit diagram or electrical model of an automatic parking brake 1 with a DC motor as actuator 2 . The actuator 2 and the input lines 13, 13' here form a load connected to the control unit. The input lines 13 , 13 ′ connected to the H-bridge circuit 9 are each shown as an input line resistance R _w , since these mainly exhibit an ohmic characteristic. The brake motor can be approximately described by the motor induction element L _mot and the coil resistance R _mot in the state of . Furthermore, DC motors usually include an anti-interference capacitor C _x , which is supposed to improve the electromagnetic radiation properties of the motor, and which is connected in parallel with the motor induction element L _mot and the winding resistance R _mot .

In the case of a short circuit _KS between the two input lines 13, 13' in the automatic parking brake system shown in FIG. Ohmic behavior of R _w , wherein a short circuit is caused, for example, by damage and contact due to damage of the two input lines 13 , 13 ′. This line resistance R _w moves in the milliohm range and therefore requires a high direct current in order to be able to distinguish between intact and faulty lines during driving and thus to detect a short circuit. However, as stated at the beginning of this article, it is also not possible to supply a very high direct current to check the functioning of the parking brake system during driving operation, since this would cause a movement of the actuator 2 and thus a movement of the actuator 2 in the event of an intact line. Generate clamping force. This possibility of detecting a short circuit is therefore limited to use during actuation of the parking brake 1 when the vehicle is parked.

Conversely, the method according to the invention enables detection of a short circuit at any time during driving operation of the vehicle without the risk of actuating the automatic parking brake 1 . The method makes use of the fact that, although the actuator 2 can be moved in opposite directions of rotation and therefore with two different current directions, due to the inertia of the actuator 2, this actuator is From a certain frequency onwards it is no longer possible to follow that frequency. If the frequency of the trigger signal exceeds a certain limit value, which is dependent on the inertia of the actuator 2, then the actuator 2 does not perform any movement despite the input of the trigger signal. The triggering signal is a current which is generated by triggering the switching elements T1 to T4 of the H-bridge circuit 9 and by providing a suitable supply voltage _Ub . As already stated, the direction of the current flow and thus the direction of rotation of the actuator 2 can be changed by corresponding activation of the switching elements T1 to T4 of the H-bridge circuit.

Movement of actuator 2 during driving operation is prevented by the high-frequency activation of actuator 2 , which also results in high-frequency polarity inversions of actuator 2 . In other words, the deactivation of the actuator 2 remains unaffected by the high-frequency trigger signal. The high-frequency trigger signal can now advantageously be used for short-circuit detection in the automatic parking brake system without the risk of actuating the automatic parking brake 1 during driving operation of the vehicle. The term "high-frequency" is currently understood to be the frequency at which the actuator 2 remains stationary due to its inertia.

FIG. 5 shows a diagram with the triggering signals of the switching elements T1 to T4 of the H-bridge circuit 9 and the resulting actuator currents measured by means of the current measuring unit 11 . The switching elements T1 to T4 are switched with a high frequency in order to generate a high-frequency trigger signal which is supplied to the actuator 2 via the lines 13 , 13 ′. In this case, the switching elements T1 and T4 or T2 and T3 are alternately switched conductive. The current direction of the trigger signal is thus switched at the same frequency. The frequency can be, for example, 25 kHz in order to safely rule out movement of the actuator 2 . The frequency of the trigger signal is also advantageously outside the human audible range, so that the vehicle occupants cannot hear the function test of the automatic parking brake system.

By generating and delivering high-frequency trigger signals, a complete functional check of the automatic parking brake system can now be carried out: as shown in FIG. During a very high AC current flow through the low impedance line resistance. This alternating current, labeled I _KS in FIG. 5 , can be detected in the current measuring unit 11 of the control unit. The measured current can be compared, for example, with a predetermined threshold value in order to thus reliably infer the presence of a very high alternating current due to a short circuit.

In the event that the motor input line 13 , 13 ′ is not short-circuited but has an interruption, no current flows in the automatic parking brake system and therefore no current is measured in the current measuring unit 11 . In FIG. 5 , the measurable current thus has the value 0 and is marked with I _break . Therefore, if the test triggering of the switching elements T1 to T4 does not result in a measurable current flow, it can be concluded that there is a line interruption in the parking brake system.

If, on the other hand, the input lines 13, 13' of the parking brake system are neither short-circuited nor interrupted, then during the test run the high-frequency triggering signal flows through the anti-interference capacitor _Cx of the actuator 2 and with a small fraction Reactive currents in the form of hundreds of mA to several amperes are detected in the current measuring unit 11 . The height of the reactive current depends here on the value of the capacitor C _x and the trigger frequency. In Fig. 5, the measurable reactive current of capacitor Cx is denoted by _IOK . This current has a periodically fluctuating shape typical for capacitors, which can be easily recognized.

Overall, therefore, three different states of the automatic parking brake system can be safely determined during driving operation of the vehicle by means of the method according to the invention by means of a high-frequency activation of the actuator 2 . The actuator current caused by the high-frequency triggering can be measured by means of the current measuring unit 11 already present in the drive parking brake system. Depending on the state of the parking brake system, three situations can arise which indicate an interruption, a short circuit or an intact condition in the system. Depending on the state of the system, the actuator current caused by the high-frequency triggering and measured by the current measuring unit 11 is zero, with a high short-circuit level or a low reactive current level. If no capacitors are provided in the actuator 2, such capacitors are retrofitted for carrying out the method according to the invention for detecting a short circuit, or another suitable passive or optionally also active component is integrated into the parking system. In the brake system and in particular integrated into the actuator 2 to detect intact conditions.

Due to the high-frequency triggering of the H-bridge circuit 9 , the risk of movement of the actuator 2 during the driving operation of the vehicle is eliminated, wherein movements could occur in the intact state of the automatic parking brake system.

In order to evaluate the measured current during the test run, a suitable algorithm can be implemented in the respective controller, which compares the measured current with a threshold value and in this way can determine the situation. The threshold value is preferably adapted here to the respective frequency used and in particular also to the parameters of the passive component (capacitor C _x ).

When an operating fault is detected, in particular in the event of an interruption or a short circuit, the driver can already signal a malfunction of the automatic parking brake system during driving operation. Furthermore, an emergency parking brake function can optionally be activated, which, for example, enables a fully hydraulic actuation of the parking brake when the vehicle is parked until operating faults of the automatic parking brake system are eliminated.

Claims (11)

1. for checking the method for the function status of automatic emergency brake system, automatic emergency brake system is with the actr (2) of control unit and the braking force for generation of electromechanics, it is characterized in that, the control unit frequency higher than the frequency that actr (2) can be facilitated to rotate triggers actr (2).

2., by method according to claim 1, it is characterized in that, measure the actr electric current caused by described triggering by current measuring unit (11).

3., by the method described in claim 1 or 2, it is characterized in that, the H-bridge circuit (9) by control unit produces high-frequency actr energizing signal.

4. by method described in aforementioned any one of claim, it is characterized in that, frequency, between 10 kHz and 50 kHz, especially preferably counts about 25 kHz between 20 kHz and 40 kHz.

5., by the method described in any one of claim 2 to 4, it is characterized in that, caused actr electric current is evaluated in the situation of the incoming line (13,13 ') of actr (2).

6., by the method described in any one of claim 3 to 5, it is characterized in that, actr (2) is transformed polarity with the frequency of high-frequency actr energizing signal.

7., by the method described in aforementioned any one of claim, it is characterized in that, in the normal operation conditions of emergency brake system, cond (C _x) especially the anti-interference condenser of actr produce the reactive component of current (I that can measure based on actr energizing signal _oK).

8., by the method described in aforementioned any one of claim, it is characterized in that, the method is performed continuously or according to periodic interval at the traveling run duration of vehicle.

9., by the method described in aforementioned any one of claim, it is characterized in that, the inertia according to actr (2) selects frequency.

10. regulate and/or controller, for performing by the method described in any one of claim 1 to 9.

11. automatic emergency brake systems in a motor vehicle, with by adjustment according to claim 10 and/or controller.